Optical device comprising a polymer actuator

ABSTRACT

The invention relates to an optical device comprising; a) a polymer film ( 101 ) comprising a first surface ( 107 ) and a second surface ( 108 ), b) a first electrode ( 102 ) mapped on said first surface ( 107 ), c) a second electrode ( 103 ) mapped on said second surface ( 108 ), d) a deformable optical element ( 104 ) mapped on said first electrode ( 102 ) or on said first surface ( 107 ).

FIELD OF THE INVENTION

The invention relates to an optical device comprising an optical elementwhich can be deformed so as to modify its optical characteristics.

The invention may be used in any apparatus or device in which opticalcharacteristics of an optical element have to be changed, such as thefocus of a lens or the pitch of a diffraction grating.

BACKGROUND OF THE INVENTION

The Patent of United States published under reference US 2001/0040735A1describes a variable-focus lens. The variable-focus lens is constructedby making small changes in the equatorial diameter of an elasticallydeformable lens. The lens may be deformed by radial tension exerted in aplane generally perpendicular to the optical axis. The radial tensionmay be exerted by mechanical means or by rings embedded in or attachedto the equator of the lens, whose diameter can be altered by heating orby the application of an electric or magnetic field.

The technique described in the prior art document not only implies theuse of complicated and numerous actuators for changing the focus of thelens, but it is also difficult to implement in small devices orapparatus.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to propose an improved optical devicefor deforming an optical element.

To this end, the optical device according to the invention comprises:

-   -   a polymer film comprising a first surface and a second surface,    -   a first electrode mapped on said first surface,    -   a second electrode mapped on said second surface,    -   a deformable optical element mapped on said first electrode or        on said first surface.

When a voltage difference is applied between the two electrodes, theMaxwell stress phenomenon causes the polymer film to lengthen in planardirection, and this elongation is transmitted to the deformable opticalelement. The optical characteristics of the optical element change asresult of its deformation.

Since the optical element is in direct contact with the polymer film,the optical device is of small size.

Since the elongation of the polymer film depends on the voltagedifference applied between the electrodes, the deformation of theoptical element is easily controllable.

In particular, said optical element is a circular lens or a diffractiongrating.

The optical device can thus be used for varying the focus of a lens orthe pitch of a diffraction grating.

In a preferred embodiment, the optical element is made of siliconerubber or made of cyclic olefin copolymer.

Such materials have characteristics that lead to a good compromisebetween optical quality and the ability to deform.

In a preferred embodiment, the polymer film is made of silicone rubberor acrylic dielectric elastomer.

Such materials allow a substantial deformation so that the opticalcharacteristics of the optical element can be modified in a largeproportion.

In a preferred embodiment, the first electrode and the second electrodehave the shape of a circle.

In a preferred embodiment, the first electrode and the second electrodehave the shape of a ring.

If electrodes are made of transparent material, a light beam can passthrough the polymer film and the optical element along its optical axis.This feature relates in particular to the circular lens.

Electrodes having the shape of rings allow the use of either transparentor non-transparent materials for the electrodes.

The invention also relates to a polymer film sandwiched between twoelectrodes intended to receive a voltage difference, for deforming anoptical element in contact with said polymer film or said electrodes.

The property of such a film and the particular arrangement of thepolymer film with respect to the electrodes is advantageously used fordeforming the optical element under an electrical control.

The invention also relates to a method of changing the opticalcharacteristics of an optical element, said method comprising the stepsof:

-   -   mapping a first electrode on a first surface of a polymer film,    -   mapping a second electrode on a second surface of said polymer        film,    -   mapping said optical element on said first electrode or on said        first surface,    -   applying a voltage difference between said first electrode and        said second electrode.

Such a method can be used for changing electrically the opticalcharacteristic of an optical element.

Detailed explanations and other aspects of the invention will be givenbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular aspects of the invention will now be explained withreference to the embodiments described hereinafter and considered inconnection with the accompanying drawings, in which identical parts orsub-steps are designated in the same manner:

FIG. 1A depicts a first embodiment of an optical device according to theinvention, in a first state,

FIG. 1B depicts the first embodiment in a second state,

FIG. 1C depicts the first embodiment in a three-dimensional explodedview,

FIG. 1D depicts an alternative of the first embodiment, in a firststate,

FIG. 1E depicts the alternative of the first embodiment in a secondstate,

FIG. 1F depicts the alternative of the first embodiment in athree-dimensional exploded view,

FIG. 2A depicts a second embodiment of an optical device according tothe invention in a first state,

FIG. 2B depicts the second embodiment in a second state,

FIG. 2C depicts the second embodiment in a three-dimensional explodedview,

FIG. 2D depicts an alternative of the second embodiment in athree-dimensional exploded view.

DETAILED DESCRIPTION OF THE INVENTION

The invention utilizes the Maxwell stress phenomenon. This phenomenonrelates to the deformation of a polymer material sandwiched between twoelectrodes. When a voltage difference is applied between saidelectrodes, the electrostatic forces resulting from the free chargessqueeze and stretch the polymer.

FIG. 1A depicts a first embodiment of an optical device according to theinvention in a first state. This embodiment comprises:

-   -   a polymer film 101 comprising a first surface 107 and a second        surface 108. The polymer film 101 is advantageously made of        silicone rubber or acrylic dielectric elastomer (for example the        elastomers referred to as NuSil's CF19-2186 and VHB 4910        acrylic). The characteristics of dielectric polymers are such        that they are soft (compliant), have a relatively high        dielectric constant (approximately 3 or more), and have a high        breakdown voltage (a few tens up to a hundred kV/mm).    -   a first electrode 102 mapped on said first surface,    -   a second electrode 103 mapped on said second surface,    -   a deformable optical element 104 mapped on said first electrode        102. The optical element corresponds to a circular lens        advantageously made of silicone rubber or made of cyclic olefin        copolymer (COC). The lens may be fixed on the electrodes        directly or by means of glue. The lens has a radius of curvature        of value r1.

This optical device is advantageously symmetrical around axis AA, whichcorresponds to the optical axis of the optical element 104.

The first electrode 102 is connected to a wire 105, and the secondelectrode 103 is connected to a wire 106. Wires 105 and 106 are intendedto be connected to a voltage difference V.

The electrodes are made of compliant (soft) material so that they candeform with the polymer film. The electrodes may be deposited viaspraying, screen printing, or photolithography. The electrodes can bemade of graphite paste, very thin metal wires, or very thin metal films.

The electrodes are advantageously made of transparent material, so thata light beam can pass through the lens, the polymer film, and theelectrodes. In that case, the electrodes are made, for example, ofmaterial known as “pdot” used in polymer LED displays.

In a second state depicted in FIG. 1B, a voltage difference V is appliedbetween the electrodes via the wires 105-106. The polymer film 101 (andthe electrodes 102-103) expand as a consequence in the radial directionsd1 and d2, in a plane parallel to the plane defined by the polymer film.As a consequence, the lens 104 also deforms, which causes its radius ofcurvature r2 to change.

The strain of the polymer film (generally of the order of several tenspercents) has a quadratic relation to the voltage difference V. It mustbe of the order of a few kV, depending on the thickness of the polymerfilm. To reduce the voltage, a multi-layered structure may beadvantageously made.

FIG. 1C depicts the first embodiment of FIG. 1A and FIG. 1B in athree-dimensional exploded view. The polymer film preferably has acircular shape so that its deformation is symmetrical in the radialdirections. Advantageously, the optical axis AA of the lens 104 isperpendicular to the plane defined by the polymer film 101.

FIG. 1D depicts an alternative of the first embodiment according to theinvention, in a first state. It differs from FIG. 1A, FIG. 1B, and FIG.1C in that the circular lens 104 is mapped on the first surface 107.Moreover, the partial area of the second surface 108 in front of theoptical lens is not covered by said second electrode. The electrodes102-103 thus form a ring centred around the optical axis AA of the lens104. This alternative allows the use of transparent as well asnon-transparent electrodes 102-103.

In a second state depicted in FIG. 1E, a voltage difference V is appliedbetween the electrodes via the wires 105-106. The polymer film 101 (andthe electrodes 102-103) expand in the radial directions d1 and d2, in aplane parallel to the plane defined by the polymer film. As aconsequence, the lens 104 also deforms, which causes its radius ofcurvature r2 to change.

FIG. 1F depicts the first embodiment as described in FIG. 1D and FIG. 1Ein a three-dimensional exploded view.

FIG. 2A depicts a second embodiment of an optical device according tothe invention in a first state. This embodiment comprises:

-   -   a polymer film 201 comprising a first surface 207 and a second        surface 208. The polymer film 201 is advantageously made of        silicone rubber or acrylic dielectric elastomer (for example the        elastomers referred to as NuSil's CF19-2186 and VHB 4910        acrylic). The characteristics of dielectric polymers are such        that they are soft (compliant), have a relatively high        dielectric constant (approximately 3 or more), and have a high        breakdown voltage (a few tens up to a hundred kV/mm).    -   a first electrode 202 mapped on said first surface,    -   a second electrode 203 mapped on said second surface,    -   a deformable optical element 204 mapped on said first electrode        202. The optical element corresponds to a diffraction grating        having a base surface advantageously made of silicone rubber or        made of cyclic olefin copolymer (COC). The grating may be fixed        directly on the electrodes or by means of glue. The diffraction        grating has a pitch of value p1.

The first electrode 202 is connected to a wire 205, and the secondelectrode 203 is connected to a wire 206. Wires 205 and 206 are intendedto be connected to a voltage difference V.

The electrodes are made of compliant (soft) material so that they candeform with the polymer film. The electrodes may be deposited viaspraying, screen printing, or photolithography. The electrodes may bemade of graphite paste, very thin metal wires, or very thin metal films.

In a second state depicted in FIG. 2B, a voltage difference V is appliedbetween the electrodes via the wires 205-206. The polymer film 201 (andthe electrodes 202-203) expand in the directions d1 and d2, in a planeparallel to the plane defined by the polymer film. As a consequence, thediffraction grating 204 also deforms along its grating vector, whichcauses its pitch p2 to change.

The electrodes are advantageously made of transparent material, so thata light beam can pass through the grating, the polymer film, and theelectrodes. In that case, the electrodes are made, for example, ofmaterial known as “pdot” used in polymer LED displays.

The strain of the polymer film (generally of the order of several tenspercents) has a quadratic relation to the voltage difference V. It mustbe of the order of a few kV, depending on the thickness of the polymerfilm. To reduce the voltage, a multi-layered structure may beadvantageously made.

FIG. 2C depicts the second embodiment of FIG. 2A and FIG. 2B in athree-dimensional exploded view. The polymer film preferably has arectangular shape having its sides parallel and perpendicular to thestructure of the diffraction grating.

FIG. 2D depicts in a three-dimensional exploded view, an alternative ofthe second embodiment according to the invention. It differs from FIG.2A, FIG. 2B, and FIG. 2C in that the grating 204 is mapped on the firstsurface 207. Moreover, the partial area of the second surface 208 infront of the grating is not covered by said second electrode. Theelectrodes 202-203 thus form a rectangular or square surrounding. Thisalternative allows the use of transparent as well as non-transparentelectrodes 202-203.

The deformation of the film polymer depends on the modulus of thematerial used, the shape of the material, as well as boundaryconditions.

The invention is not limited to the shapes described for the polymerfilm. Indeed, other shapes could be defined for deforming in anon-uniform way the optical element mapped on said polymer film.

The invention also relates to a polymer film sandwiched between twoelectrodes for deforming an optical element.

The invention also relates to a method of changing the opticalcharacteristics of an optical element, said method comprising the stepsof:

-   -   mapping a first electrode on a first surface of a polymer film,    -   mapping a second electrode on a second surface of said polymer        film,    -   mapping said optical element on said first electrode or on said        first surface,    -   applying a voltage difference between said first electrode and        said second electrode.

1. Optical device comprising: a polymer film (101) comprising a firstsurface (107) and a second surface (108), a first electrode (102) mappedon said first surface (107), a second electrode (103) mapped on saidsecond surface(108), a deformable optical element (104) mapped on saidfirst electrode (102) or on said first surface (107).
 2. Optical deviceas claimed in claim 1, wherein said optical element (104) is a circularlens or a diffraction grating.
 3. Optical device as claimed in claim 1or 2, wherein said optical element (104) is made of silicone rubber orof cyclic olefin copolymer.
 4. Optical device as claimed in claim 1, 2or 3, wherein said polymer film (101) is made of silicone rubber oracrylic dielectric elastomer.
 5. Optical device as claimed in claim 1,2, 3 or 4, wherein said first electrode (102) and said second electrode(103) have the shape of a circle.
 6. Optical device as claimed in claim1, 2, 3 or 4, wherein said first electrode (102) and said secondelectrode (103) have the shape of a ring.
 7. Polymer film (101)sandwiched between two electrodes (102, 103) intended to receive avoltage difference, for deforming an optical element (104) in contactwith said polymer film (101) or said electrodes (102, 103).
 8. Method ofchanging the optical characteristics of an optical element (104), saidmethod comprising the steps of: mapping a first electrode (102) on afirst surface (107) of a polymer film (101), mapping a second electrode(103) on a second surface (108) of said polymer film (101), mapping saidoptical element (104) on said first electrode (103) or on said firstsurface (107), applying a voltage difference between said firstelectrode (102) and said second electrode (103).